Modelling of Fe-Cr Martensitic Steels Corrosion in Liquid Lead Alloys

Among the Generation IV systems, Sodium Fast Reactors (SFR) are promising and benefit of considerable technological experience. However, the availability and the acceptability of the SFR are affected by the problems linked with the sodium-water reaction. One innovative solution to this problem is the replacement of the sodium in the secondary loops by an alternative liquid fluid. Among the fluids considered, lead-bismuth is at the moment being evaluated, liquid lead-bismuth has been considerably studied in the frame of the research program on Accelerator Driven Systems for transmutation applications. However, lead alloys are corrosive towards structural materials. The main parameters impacting the corrosion rate of Fe-Cr martensitic steels (considered as structural materials) are the nature of the steel (material side), the temperature, the liquid alloy velocity and the dissolved oxygen concentration (liquid alloy side). In this study, attention is focused on the behaviour of Fe-9Cr steels and more particularly T91 martensitic steel. It has been shown that in the case of Fe-Cr martensitic steels the corrosion process depends on the concentration of oxygen dissolved in Pb-Bi. - For an oxygen concentration lower than the one necessary for magnetite formation (approximately < 10⁻⁸ wt% at T ≈ 500 °C for Fe-9Cr steels), corrosion proceeds by dissolution of the steel. - For a higher oxygen content dissolved in Pb-Bi, corrosion proceeds by oxidation of the steel. These two corrosion processes have been experimentally and theoretically studied in CEA Saclay and also by other partners leading to some corrosion modelling in order to predict the life duration of these materials as well as their limits of utilisation. This study takes into account the two kinds of corrosion processes, dissolution and oxidation. In these two different processes, the lead alloy physico-chemical parameters are considered: the temperature and the liquid alloy velocity for both processes and the oxygen concentration for oxidation.